This is a revised application (A2) for interdisciplinary behavioral, neuroendocrine and neuroimaging studies of sex differences in response to nicotine submitted in response to NIDA PA-07-329. Among the addictive disorders, nicotine addiction is one of the most pervasive, and is associated with a number of potentially lethal diseases (lung cancer, cardiovascular and respiratory disease) that result in an estimated 448,000 deaths each year. Improved treatments for nicotine addiction are urgently needed, and will be facilitated by advances in our understanding of the basic neurobiology of nicotine. We propose clinical studies to examine the covariance between the hormonal, behavioral and neuroimaging effects of nicotine in nicotine- dependent men and women to determine if there are significant sex differences. Women will be studied during the mid-follicular and the mid-luteal phase of the menstrual cycle to determine if the effects of nicotine are influenced by changes in the neuroactive gonadal steroid hormones that define phases of the menstrual cycle. Functional magnetic resonance imaging (fMRI) will be used to study regional changes in brain activity. The effects of IV nicotine and placebo nicotine on neuronal activity in brain areas with a high density of nicotinic receptors, and also in regions that may be important drug reward pathways will be measured over time, and correlated with subjective and hormonal responses. Nicotine (0, 1.0 or 2.0 mg/70 kg, IV) will be administered under double-blind conditions. Samples for analysis of hypothalamic-pituitary-adrenal and gonadal hormones will be collected every 2 min to examine the temporal covariance with neuroimaging activation patterns and reports of subjective effects. We hypothesize that neuronal and hormonal activation and positive subjective responses to IV nicotine administration will be greater in men than in women. We also hypothesize that women will have greater neuronal and hormonal activation and positive responses to nicotine during the follicular phase of the menstrual cycle (when neuroactive steroid hormone levels are low) than during the luteal phase of the menstrual cycle (when neuroactive steroid hormone levels are high). Because the neuroactive steroid hormones are being used to treat a number of psychiatric disorders including drug abuse, this could lead to novel treatments for nicotine addiction. The results of these translational studies will increase our understanding of the interaction between sex, hormones, and the abuse-related effects of nicotine. These interdisciplinary studies will integrate behavioral, hormonal and neuroimaging measures to provide a comprehensive analysis of how sex differences and phases of the menstrual cycle may affect the abuse- related effects of nicotine. Advances in understanding the basic neurobiology of nicotine will inform efforts to develop better pharmacologic interventions to treat nicotine addiction.